CK-12 Physical Science - For Middle School

7.2. Ionic Bonds http://www.ck12.org

ion always comes first. For example, sodium and chloride ions form the compound named sodium chloride.

You Try It!

Problem: What is the name of the ionic compound composed of positive barium ions and negative iodide ions?

Properties of Ionic Compounds

The crystal structure of ionic compounds is strong and rigid. It takes a lot of energy to break all those strong ionic
bonds. As a result, ionic compounds are solids with high melting and boiling points (seeTable7.2). The rigid
crystals are brittle and more likely to break than bend when struck. As a result, ionic crystals tend to shatter. You
can learn more about the properties of ionic compounds by watching the video at this URL: http://www.youtube.c
om/watch?v=buWrSgs_ZHk (3:34).

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/5081

Compare the melting and boiling points of these ionic compounds with those of water (0°C and 100°C), which is
notan ionic compound.

TABLE7.2:Melting and Boiling Points of Select Ionic Compounds

Ionic Compound Melting Point(°C) Boiling Point(°C)

Sodium chloride (NaCl) 801 1413

Calcium chloride (CaCl 2 ) 772 1935

Barium oxide (BaO) 1923 2000

Iron bromide (FeBr 3 ) 684 934

Solid ionic compounds are poor conductors of electricity. The strong bonds between ions lock them into place in
the crystal. However, in the liquid state, ionic compounds are good conductors of electricity. Most ionic compounds
dissolve easily in water. When they dissolve, they separate into individual ions. The ions can move freely, so they
are good conductors of electricity. Dissolved ionic compounds are called electrolytes.

Uses of Ionic Compounds

Ionic compounds have many uses. Some are shown inFigure7.6. Many ionic compounds are used in industry. The
human body also needs several ions for good health. Having low levels of the ions can endanger important functions
such as heartbeat. Solutions of ionic compounds can be used to restore the ions.

Lesson Summary

• An ionic bond is the force of attraction that holds together oppositely charged ions. It forms when atoms of
  a metal transfer electrons to atoms of a nonmetal. When this happens, the atoms become oppositely charged
  ions.